Is there a W3C document that states the requirements on all XMLapplications regarding character encoding mismatches?

From: "Costello, Roger L." <costello@mitre.org>

To: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>

Date: Fri, 18 Jan 2013 10:48:43 +0000

Hi Folks,
Issue: document #1 specifies encoding="A". It processes document #2, which specifies encoding="B". There is a character encoding mismatch. Encoding conversion is required.
Definition: an "XML application" is an application that processes XML documents. Examples of XML applications include XML parsers and XSLT processors and XML Schema validators.
Question: does the W3C have an over-arching document that gives the requirements on all XML applications with respect to character encoding conversion requirements when there are encoding mismatches?
Here are a few places where character encoding conversion is needed due to encoding mismatches:
1. An XML document specifies encoding="A" and it contains an external ENTITY reference to a document that has encoding="B". The XML parser must recognize this mismatch and convert the character encoding of the external document into the character encoding of the XML document.
Or perhaps the XML document is converted to the
character encoding of the external document?
2. An XSLT document specifies encoding="A" and its input document has encoding="B". The XSLT processor must recognize this mismatch and convert the character encoding of the input document into the character encoding of the XSLT document.
Or perhaps the XSLT document is converted to the
character encoding of the input document?
3. An XML document specifies encoding="A" and is validated against an XML Schema that has encoding="B". The XML Schema validator must recognize this mismatch and convert the character encoding of the XML document into the character encoding of the XML Schema document.
Or perhaps the XML Schema document is converted
to the character encoding of the XML document?
Can you think of other examples where character encoding mismatches may occur and conversion is necessary?
This issue is broader in scope than just XML, as it concerns all XML applications. So I would not expect to see the XML specification to address this issue. I would expect an over-arching uber-document to address this. Is there such a document?
/Roger